|For deformed tunnels, it is necessary to carry out appropriate repair work and reinforcement work according to the state of defects and deformation, in order to ensure the structural stability of the tunnel and the safety of users. For that purpose, advanced tech
nical judgment is required to accurately and reliably grasp the mechanism and factors of the defects. In this paper, we focused on the ultrasonic velocity on the lining surface as one of the methods for supporting to grasp the condition of the tunnel lining. The relationship between the strain and the ultrasonic velocity of the lining surface was examined by the full- scale lining loading experiment, and the ultrasonic velocity in the actual tunnel was
ured. The possibility of estimating the stress state of the lining was also examined based on the results.